This invention relates to shaft couplings, and more particularly to improvements in couplings of the type that use a grid of metal rungs to join coupling halves.
A common form of flexible coupling used for joining driving and driven shafts utilizes a metal grid to join coupling halves mounted on the shafts being coupled. The grid is often formed as a serpentine with straight grid rungs joined together at alternate ends by integral end loops. The rungs are received in axially aligned, radially extending slots formed between metal teeth on each of the coupling hubs. The rungs span the space between the coupling halves and act to transmit torque between the hubs. The side walls of the teeth are generally curved in an axial direction so that the unsupported length of each rung is reduced as the torsional load transmitted between the coupling halves increases. An early example of this type of flexible coupling is found in U.S. Pat. No. 1,763,842 issued June 17, 1930 to Bibby.
In the prior flexible couplings of this type, the rungs and the hubs are made of metal, usually steel, and the rungs are heat treated.
This form of flexible coupling provides an effective device for joining shafts, but because of its construction it may be too stiff in its response to torsional load. There are applications for shaft couplings in which significantly less stiffness would be desirable.
Attempts to reduce the stiffness inherent in this type coupling have in the past focused on altering the form of the grid or of the tooth curvature to make them more flexible. Prior efforts have included using straight metal rungs joined at their ends by elastomer members (U.S. Pat. No. 4,413,980 issued Nov. 8, 1983 to Walloch), using complementary closed loops (U.S. Pat. No. 3,196,635 issued Jul. 27, 1965 to Schmitter), and using alternate U-shaped spring grid elements (U.S. Pat. No. 2,555,909 issued June 5, 1951 to Wellauer).
It is noteworthy that thus far no efforts have been put forth toward altering the composition of the teeth of the hubs for the purpose of increasing the flexibility. In particular, no attention has apparently been directed to altering the material of the hubs to reduce the stiffness of the teeth.
In the prior flexible couplings using metal grids working against metal hubs, it is typical that all grid rungs and all teeth will not carry the same load because of variations in the circumferential tooth spacing that are inherent in the manufacturing process. As a result, one or more rungs may be out of contact with a tooth and, therefore, will not carry any load. Thus far, the inherent flexibility of the grid has been relied upon to eventually, at high load, evenly distribute the load between all rungs and all teeth.